It is proposed to use conditional and nonconditional mutants of Chlamydomonas reinhardtii to study structure and assembly of flagella. Among nonconditional mutants are those with defects in various flagellar substructures. Flagella from these mutants when analyzed by two-dimensional polypeptide mapping methods will provide knowledge of the polypeptide composition of the substructures. The use of revertant analysis and a new technique of dikaryon rescue will identify protein molecules which are critical for assembly of a part or of an entire structure.